An effective way to wake up a sleeping person is to generate an alarm that simulates a telephone call. The reason is because the sound of a telephone ring can usually attract attention more easily and because a sleeping person may have more difficulty in ignoring the telephone ring before he/she can ascertain that the telephone ring is not the result of a real telephone call.
Although prior art alarm clocks have used a telephone set to generate an alarm, they have been found to be unsatisfactory. For example, these prior art alarm clocks generally require modifications to the telephone set and therefore cannot work with existing telephone sets.